The United States is planning to send six F-22 Raptor stealth fighter jets to a joint air force exercise in South Korea next month in what is believed to be US action to put maximum pressure on North Korea, military officials here said on Thursday.

"Six F-22 fighters from the US Air Force are scheduled to join the joint South Korea-US air force exercise Vigilant Ace from Dec. 4-8," the officials said.

The fighters will fly to the Korean Peninsula from Kadena Air Base in Okinawa, Japan and stay at an air base in South Korea throughout the exercise, according to officials. Up to four F-35A Lightning stealth fighters are also likely to join the deployment, they said.

The US fleet will reportedly engage in enemy infiltration and precision strike drills with South Korean Air Force fighter jets during the exercise.

It would mark the first time the US has deployed six Raptors to Korea at once and is sure to put pressure on North Korea with the overwhelming military force by the allies.

The Raptor, an air superiority fighter, is capable of flying to key enemy facilities and launching precision attacks under the radar. Its maximum speed is about Mach 2.5.

The planned deployment comes as the US steps up the deployment of strategic assets to South Korea in a show of force aimed at pressuring North Korea to the maximum level. Early this month, three US nuclear-powered aircraft carriers were deployed to the East Sea after powerful American fighter jets flew near North Korea in the previous months.

South Korea and the US are escalating pressure, both economic and military, on North Korea in efforts to bring the country back to the table to negotiate its illegal development of nuclear weapons.

The move is also sure to lead to an angry reaction from North Korea and threats to retaliate as similar operations have done in the past.